Phase corrector for telegraph systems



Feb. 2, 1943 w. AHANDERSON PHASE CORRECTOR FOR TELEGRAPH SYSTEMS 2 Sheets-Sheet 1 Filed April 30 Arr'oRNEY Feb. 2, 1943 w. A. ANDERSON PHASE CORRECTOR FOR TELEGRAPH SYSTEMS 2 Sheets-Sheet 2 Filed April 50, 1941 INVENTOR ATTORNEY Patented Feb. 2, 1 943 asoatzz PHASE commc'ron FOR TELEGRAPH SYSTEMS,

Warren A. Anderson, New Dorp, Staten'Island,

N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application April30, 1941, Serial No. 391,077

; 6 Claims. (01. 178-695) This invention relates to improvement in a phase corrector for a telegraph system and has particular reference to a device for maintaining a receiving distributor in phase synchronism with the speed of reception of telegraph signals. Whenever the periodic rate of operation of a receiving device drifts out of step with the'rate at which the incoming signals are applied to such a device, it is necessary to produce a corrective action so as to either retard or accelerate the speed of the receiving, distributor or other receiving apparatus. been used in the past it has been common practice to obtain a corrective action by the use of the signal elements themselves in combination with locally derived pulses such as may be produced, for example, by means of a local distributor. In the early stages of design of phasecorrectors a comparison was made between the moments of passage of a distributor brush over a given synchronizingsegment and the moments of arrival of the front edges of the marking signal impulses.

- The distributor speed was accordingly-adjusted In phase correctors such as have to compensate for departures from synchronism as determined solely by the front edges of the marking signals and without reference to varia tions in the elongation or other distortion of said signals.

More recent improvements in the art of phase correction are disclosed in U. S. Patent #2',2l2 ,44'7,-

' It is an-object of my invention to improve upon the structures and methods of operation disclosed in the foresaid cases of Mathes, Clark and Shenk by providing a more dependablearrangement, the operating characteristics of which are not seriously affected by normal distortion of 4 signals.-

7 Itis another object of my invention to provide means for measuring two relatively short time intervals one of which elapses between the front edge of a marking signal and a localimpulse, and

the other of which elapses :between a second local impulse and the end of the marking signal, where the two said local impulses occur'equidistant from the normal center of a time allotment for dot unit impulse reception-and where a comparison of the two said time intervals may be utilized for phase correction purposes.

It is still another object of my invention to pro vide a phase correction circuit having output terminals which may be connected to any one of a number of different utilization devices, particularly those which might be used in a multiplex telegraph system or in asimplex telegraph system, all of which devices are to be maintained in synchronism with the periodic rate of reception of incoming signals.

My invention will now be described in detail, reference being made to the accompanying drawings in which Figure 1 shows diagrammatically a preferred circuit arrangement including the essential elements in combination for carrying out the invention; and a Figs. 2 to 6 inclusive are plots of electrical impulses which occur in various parts of the circuit arrangement. These plots are all drawn to the same horifzontal time scale in order to show a correlation of essential operations in response to signals. i

In the following description of the circuit ar-' rangement of elements referenced VI, V2, V3, etc., will be understood to be vacuum discharge tubes of one type or another. Elements referenced Il, T2, T3, etc., will be understood to be discharge tubes of the gas-filled ionization discharge type. These tubes are conventionally indicated by means of a black spot in the discharge zone. Resistors wherever referenced will be given numbers of theseries Rl', R2, R3, etc., while capacitors will be referenced 0!, C2, C3, etc. Speciflc reference to each of the tubes, resistors, and

capacitors will, therefore, for'the sake of brevity,

be frequently made by their identifying symbols alone.

A comprehensive idea of the circuit arrangement and its functions will first be given by point- 1 ing out that the various-tubes and their circuit connections are arranged to make comparisons. between two capacitive charges stored in a pair of capacitors CIS and C. If an accelerating correction is to be provided because. the-local impulses are retarded in relation. to the reception of the incoming signals, then the charge stored on .Cl'l will be greater than that stored on Cl6, with the result that, during the next succeeding spacing signal, when these charges are caused to controlthe respective triode grids band a of tube V4, thenthe left hand winding of differential relay it will be so energized as todraw the relay armature 22 over to contact 23. On the other hand, if the local impulses are to be retarded because of the delay in reception of the incoming signals, then capacitor Cli will have received a greater charge than Cl 1 and during the next succeeding spacing signal a greater current flow in the left side than in the right side of V4 will cause the relay 2| to throw its armature 22 over to the contact 24. The manner in which the correction control circuits connected to terminals 6, I and 8 may be utilized will be well understood by those skilled in the art.

Referring now in more detail to Fig. 1, I show a pair of input terminals l and 2 which receive a constant frequency alternating current from a local source of oscillations the phase of which may be rotated by means of the phase correction circuit, which is the subject matter of this invention. I also show a terminal 3 to which is applied negative impulses with respect to ground, these impulses corresponding to the marking elements of the received signals.

In describing Fig. 1 a certain sequence of operations will be outlined which takes place during the reception of a single normal length baud arriving at the receiving point in proper phase, so that no correction is necessary. The operation of the system under various conditions and when the marking signals are of different lengths will At-the time of occurrence of the start (herein after designated A) of a marking pulse, a sharp rise of voltage on the anode a of V5 produces a positive pulse by differentiating a rectangular" wave through capacitor C26. This pulse is applied to the grids of gaseous tubes T3 and T6. The application of the grid control potentials just mentioned is made through grid resistors Rll and R461 respectively. An ionization discharge takes place in both of the tubes T3 and T6, but in T8 it isonly momentary because its anode receives its positive voltage solely from a charge previously stored in the capacitor C". As soon as this capacitor becomes discharged to below the extinction voltage of tube TI (say 16 volts, for example), the discharge in Tl ceases.

The discharge in T3, however, continues until it is extinguished in a manner presently to be described. The anodes of TI and T4 are intercoupled through Cl! so that when either of these tubes ignites, a surge impulse across Cl! lowers the potential on the anode of the other tube momentarily below .the point of extinction of the discharge therein. In the tube which is extinguished ther ceases to be a potential drop through the appropriate one of the resistors R or R", and the anode voltage is, therefore, raised to the full value of the +13 source. H

In accordance with the precedingparagraph the discharge in T3 causes T4 to be extinguished by commutation through the medium of Cl I and the anode potential of TI rises to full +IB value. This +3 voltage then starts char ing Cl! throu h one section of the double diode VII. This charge will continue until the occurrence of a local impulse (hereinafter termed BD which ignites TI. The charging period for 0", therefore, represents a so-called front edge integrationperiod extending from themomentAto the moment 3. A second local impulse. (hereinafter termed C) is used to mark the commencement of a back edge integration period terminating at the moment'D at the back edge of the marking signal. The impulses B and C occur normally at equal intervals preceding and following the normal center of a baud. Their timing is primarily C pulses will now be further explained. The

voltage having the 42 cycle frequency of the local source is applied across C2 to the grid In in the triode section of VI where it is amplified. Correspondingly the same voltage is applied across resistor R29 through capacitor CID to the grid IS in the triode section of V6 where it is amplified.

' V6 has functions corresponding to those of VI.

The only differencein their operation is in the phasing of the voltages applied thereto. Resistor HIV is preferably adjusted so that the signaling baud will be. divided into three approximately equal intervals by the B and C pulses.

The pentode section of VI is controlled by output from the triode' section thereof. The pentode section produces a rectangular wave shape in its anode circuit which is applied across resistor R8 'and is caused to control the grid l2 of V2 by means of surge impulses through C4 and R! on the occurrence of the steep fronts of the square wave. The output from the pentode section of tube V2 consists, therefore, in surge impulses which are applied through C5 and RH to the grid ll of V3. These applications of the surge impulses are, however, limited to marking periods because only during the marking periods is the grid l2 biased above cut 011'. Its biasing circuit is one which includes the potentiometer elements R8 and R9 in circuit with the anodeof the triode section in V2. It will be recalled that this trlOde section is biased to cut-off in the presence of a marking signal and consequently the rise of its anode voltage to full +B value produces a potential drop in R9 and R8 sufficient to render the pentode section of the same tube conductive. The shaping and limiting action of V2 will, therefore, be apparent to those skilled in the art. Tube V3 reverses both the B-pulses and the C-pulses,. where grid I4 is controlled by the B-pulses and grid I5 is controlled by the C-pulses.

The functions of VI and V1 in translating the local oscillations into c-pulses will be apparent from theforegoing description of VI and V2. However, the operation .will be briefly outlined as including the control of the triode section of V by applicationof the local sine wave to the grid I 0, so that the.amplifled current through Rid-and the anode a may be used tolcontrol the grid II in thepentode section of VI, coucause. the grid I I in the triode section of V1 to the'impulses formed in the circuit of CH.

The surge impulses derived from the pentode section of V1 are impressed across (M3 to the grid IS in the tube V3. Reversal of these impulses is then obtained in that output circuit of V3 which includes its anode b.

The B-pulses are now impressed across C6 and through the switch 32 to atap-on the negative bias potentiometer consisting of elements R42 and R43, thus controlling the grid in T4.

Simultaneously the grid of TI is also controlled by these B-pulses fed to a tap onpotentiometer Rl4, Hi5. Likewise the C-pulses delivered through R39 to the output circuit including anode b in V3 are impressed through to a tap between the elements R20 and RH ofa potentiometer 'in the grid circuit of T5. Thus the surge impulse which occurs at the moment B causes Ti and T4 to ignite, whereas the surge impulse which occurs at the moment C causes T5 to ignite.

of resistors RH and R42 are connected to the negative terminal of a grid biasing source indicatedas C.

TI having been ignited by the B-pulse the reduction of its anode voltageu'pon ignition produces a surge impulse through 01 and causes tube T2 to be extinguished. The anode of T2 then rises to full +B value and CIB starts charging. Successive charges on CIG (one being between the first B-pulse and the next C-pulse; and other charges being between successive C- pulses within the lapse of a single marking period) are wiped out by the ignition of T5,..aspreviously explained. The true back-end integration period is measured, however, by a charge stored in GIG-which started at the last C pulse with a C-pulse which immediately precedes the back end of a marking 'signal the length of which may be either one baud or a plurality of bauds. CIB may, therefore, be charged and discharged repeatedly during a long marking signal, but only the charge .which is stored thereon between the last C-pulse and the moment D, (at the back edge of the marking signal) will be used in the comparison of the integrating peri-- ods. The momentary ionization of T5 provides a discha'rge'path for CH5 such as to reduce the charge thereon down to a reference level (say,

16 volts), which is just below the extinction voltage of T5. A a

Two sources of grid excitation pulses are used for ionizing T5, one being the C -pulse which is caused to surge through CH, and the other being an effect of the first B-pulse which appears during the lapse of a marking signal. This first B-pulse is the one which ignites T4 and e'xtinguishes T3 by commutation across Cl5. The sudden increase in anode voltage in T3 produces a surge impulse through C44 and the grid (resistor R2l, thus causing T5 to ignite. By discharging vCIG through T5 both at 'the moment of the first B-pulse, and also in response to each a successive C-pulse,.a risk is avoided where the corrective action-might fail due to the splitting of the marking signal. In such case a spurious spacing condition might appear just at the moment .when the C-impulse is to be rendered ef;

fective. This would cause two or more charges to be superposed on 016.

- I have stated thatin response to the B-pulse a voltage rise takes place on the anode a of V3 which produces a surge impulse through ,ca-. pacltor C6 and causes tubes TI and T4 to ignite. This impulse 'aiiects the voltage drop across resistors R14 and R|5 and also across. resistors R42 and R43. The outer terminals of RIB and R43 are connected to the grids of the tubes in question, ,whereas the outer terminals Tl then quenches T2 and condenser Cl 6 immediate'iy starts charging. The' front-end B pulses and ended at the moment D, at the end of the marking signal. The charge is stored by virtue of the unidirectional passage of current through the upper section of the diode VII). This charge is conducted from the upper cathode in VIO through R23 to one terminal of CIG, the other terminal being grounded.

Removal of the rectified signal causes the anode a of V5 to draw current. Due to the selective action of the network R26, 08, R2'[ a short sharp pulse is applied to the grid" 5 of V5 at the moment D when transition -occursbe-- tween mark and space. Under. control of grid 5 in V5, which has been passing currentya momentary cut off condition occurs producing a positive pulse on the anode b of V5. This pulse (termed the D-pulse) controls the grid of T2 through capacitor C9 and resistor R".

The D-pulse ignites T2 which extinguishes Ti by a commutation. The anode of T2 is reduced to the tube-drop voltage which is below the voltage acquired by capacitor Cl6 during its charging period, but \the latter cannot discharge through VII]. The back end integration period is thus represented by a voltage stored in CIG for i utilization in the ensuing space period. This voltage is substantially proportional to the time I period between the last C pulsein the mark and the end thereof. i

The way condensers CIS and CH are charged and discharged upon receipt of single and multiple 'marks may be summarized as follows:

The start-of-mark A pulse discharges the front-end condenser CI! to reference level by firing T6. This pulse simultaneously fires T3. which quenches T4 and starts the condenser to ,recharge. Firing of T3 discharges condenser 1 044. This latter action has no immediate effect, I

but it places the circuit in condition to discharge back-end condenser CH5 when the first front end A pulse occurs. The first front-end A pulse fires T4 and stops the charging of front-end condenser CI 1'. All subsequent B pulsesin multiple baud marks,.as in Fig. 5, do not affect the front-end condenser C", as T4 remains conducting after the first baud, being quenched by the previous start-of-mark A pulse. The firing of T4 also quenches T3 and thisfires T5, because of the drop in R20 produced by the charging of condenser C44. Back-end condenser Cit then discharges to reference level. This first B pulse also fires Tl, the previous end-of-mark D pulse havingquenched it by firing T2. The firing of subsequent to the first one in multiple baud mark (Fig. 6') cannot discharge the back-end condenser Cl6, as T3 remains quenched until the next start-of-mark pulse'A. The first and all other back-end C pulses in the marks discharge condenser CIG to reference level by firing T5 by the drop fromthe charging current of condenser Cl4. Condenser CIG starts immediately to recharge because the first front-end B pulse quenched T2 by firing TI and it remains quenched until the occurrence of the next endof-mark pulse D. The back-end C pulse affects only condenser C11, since it controls only thyratron T5. Finally, the end-of-mark D pulse stops the charging of condenser Cl6 by firing T2.

Fig. 6 shows a time graph of the charging and discharging operations on CIG during a marking signal which persists for a period of three bauds. This may be compared with the charging of C" as shown in Fig. 5, both graphs being drawn to the same time scale.

The voltages stored in condensers CI 6 and CIT are applied through resistors R48 and R5| respectively to the two grids a and b of output.

tube V4. This storage continues during a spacing period. Tube V4 is unblocked during the spacing period by removal of the rectified signal bias so that the stored voltages on the capacitor Cl 6 and CH may be efiective. The two sections of the tube V4 will draw plate current in proportion to the voltagesstored on their respective condensers CI6 and CH. In the assumed case, the cur- 42-cycle' impulses and the phase correcting terminals I and 2 will, therefore, not be disturbed.

When a frequency difference exists between the transmitting and receiving frequency standards, or if the ether path introduces changes in the length of the signal baud, then the voltages as stored on condensers CIS and CI! will not be equal, and hence the voltages applied to the grids a and b of tube V4 will be such as to cause the anode current in one section to exceed that in the other. The differential relay 2| will then be actuated and the throw of its armature 22 to one side or the other will close the proper circuit for accelerating or retarding the phase-rotating device until the voltages on CIS and CH are again equal.

The integrating network in the anode circuit 3 of the output tube V4 prevents the operation of the differential relay on single isolated voltage differentials on GM and CH and, therefore, produces smoother operation. This network comprises series resistors R54 and R55 and shunt capacitors CIB, Cl9, C20 and CZI.

breakdown of this tube is adjusted'by means of a potentiometer R68. In order to adjust the potentiometer R66 properly a momentary break switch 32 is introduced in circuit between C5, R42 and R43. The effect of a splitting signal may be simulated by artificially interrupting the grid control of T4 so as to prevent its normal ignition. The momentary break switch 32 is used for this purpose. The voltage across Cl'l will then rise to an excessively high value. By oscilloscope observation R66 may then be adjusted so that the voltage across CI! will be dropped to the normal average and excessive correction will not take place.

It is desirable to discuss at this point the theory and principles of phase correction as applied to the synchronization of receiving telegraph equipment, and to consider the practical tolerances within which the sensitivity of the phase corrector should be adjusted.

Richard E. Mathes, in his copending application Serial No. 376,870, filed January 31, 1941, has described a system for rotating the phase of a sine wave through any angle greater or less than 360 for purposes of synchronizing a local source with a remote source. Other systems of phaserotation are, however, known in the art..

Assuming, therefore, that a local oscillator is provided which delivers impulses at a convenlent synchronizing frequency, say 42 cycles per second. then the output from such as oscillator may be fed through a phase rotator and thence to the terminals I and 2 of Fig. 1. By the aid of the correction circuit shown completely in Fig. 1 the orientation of the phase rotating device may be brought about so that the output from the phase rotator shall at all times be maintained in synchronism with a train of received signals from a remote transmitter. The phase corrected source may be applied not only to they terminals l and 2, but also to any synchronous motor which drives a receiving commutator or other apparatus used at the point of reception of teledepends upon the adjustment of the phase dif- A neon lamp 3i is connected in shunt with split will produce a spurious A-pulse which will -ignite tubes T3 and TE /CH will then be discharged to the referencevoltage whereupon T6 will self-extinguish. on will then start chargingand continue until the next B-pulse OCCUISJ' The voltage on C" wouldytherefore, rise conferentiating network Cl-'-Rl, which controls the separation between the B-pulses and the C-pulses. single-phasesine wave energy applied to terminals l and 2. .The positioning of the B-pulse and the C-pulse about the center of the'baud, on the other hand, is a function of the phase "rotating device which operates under control .of

the relay 2|. This operation tends to equalize the charges on CIS and OH. I have found, however, that the optimum spacing between the B-pulse and the C-pulse is one wherein th'ese pulses divide an elementary baud interval into three. equal parts.) The reason for this is explained as follows, reference being made to Figs.

1 2 and 3, where a marking signal of a singlebaud length is graphically represented.

Let it be assumed first that the B-pulse and the C-pulse are substantially coincident in the center-of a normal baud and that a signal elongation of 25% of the baud takes place., This tinuously even during the spacing'period when the output tubes are unblocked if the marking period was of one baud length, This would re-f Y suit in spurious correction were it'not for the operation of the neon tube 3|. The point of elongation is indicated by cross-hatching. Then the resultant front-end integration period will be measured by thex interval AB amounting to 50% of a normal baud, whereas the back end integration period will be measured by the interval C- D which is a total of 75% of a normal baud. 'In this case the voltages stored in Oil and tilt respectively are in the ratio 2:3.

These pulses are derived from the Now, let the local pulses be shifted so that the time of their occurrence is as shown at B and C in Fig. 3.. Assume also that the same 25% elongation of the signal occurs. In this case be seen that the back end integration voltage is twice as large as the front end integrationvoltage- It can, therefore, be said that the closer the locally generated pulses are positioned with respect to the start and finish of the normal baud, the more efiective will be the changes from normal in producing large correction difi'erentials; However, other diificulties arise in attempting 'to shorten the integration periods too much. Firstly, the stored voltages on capacitors Cl! and CIS become inadequate to properly operate the two sections of the output tube V4. Secondly, a division of the baud into approximately three 'equal parts by the B-pulse and the C-pulse has the effect of minimizing spurious performances of the correction circuit under conditions of excessive elongation or excessive curtailment'of the marking signals.

- The maximum time interval between the B-pulse and the C-pulse should not be so great as to extend beyond the limits of an expected shrinkage in the duration of a signal, dot.= Also the minimum time interval between the B-pulse and the C-pulse should not be so small as to be less than the maximum expected elongation of the signal.

These considerations are demonstrable by plotting the B-pulse and the C-pulse at various rector circuit arrangement thereby to actuate on the first said storage unit and the other of said n points along a graph of the marking band, and a by assifining certain departures from synchron- 'ism such as would cause either the B-pulse alone or the C-pulse alone to appear within the interval of a marking baud. The storage of incorrect and incomparable voltages in CH5 and C" under these abnormal conditions would be obvious. There is, nevertheless, a permissible range of adjustment of the spacing between the B-pulse and the C-pulse which aflects the sensitivity of the corrector circuit under various pracproducing a synchronizing efiect upon saidphase said phase rotating device in' either direction.

2. Apparatus for synchronizing the sine wave output from a phase rotator witha train oi telegraph signals, comprising a phase corrector cir- .cuit arrangement of the type which includes capacitive storage means for comparing the lengths of two time intervals having a significance such that synchronism of said sine wave output with said signals is denoted by equality of said time intervals, means in said phase corrector circuit arrangement for starting a charge on one unit of said storage means'at theftont edge of a marking signal and for terminating a charge on a second unit of said storage means at the back edge of said marking signal, a phase splitting network receptive of said sine wave output from the phase rotator, two pulse generators so controlled r by said network that one of them. is caused to deliever a control pulse for terminating the charge pulse generators is caused to deliver a control pulse for starting the charge on'the second said 7 storage unit, .means for so adjusting said phase splitting network that it causes the action of the first said pulse generator to anticipate that of the second said pulse generator by substantially one third of a cycle of said sine wave, and a.utilization device including a diiferential relay operable in accordance with the compared charges on said N storage units for performing the synchronizing function of said apparatus.

3. Apparatus according to claim 2 and including means for discharging the respective units of said'capacitive storage means down to a predetermined reference voltage. atthe inception of each of the two time intervals to be compared,

and further means for discharging the second unit'of said storage means to the same reference voltage in response to the pulse delivered by that one of said generators which terminates charge on the first said storage unit.

4. Apparatus according to claim 2 and including a'gaseous discharge tube in shunt with one of the units of said capacitive storage means and having a breakdown resistance value such as to be ionizable only when the charge on said unit exceeds a usable value.

5. A phase corrector circuit arrangement having a pair of input'terminals adapted to receive an adjustably phased sine wave, a phase splitting.

1 network connected to said terminals, a rectified rotating device, means including three pulse generators A, B, and C for determining the charging times of said capacitors, said generators being so arranged and connected that generator A is recaptive of signals from said signal input terminal and defines the starting moment of the charge on' one of said capacitors and also the finish mo- I ment of the charge on the second of said capacitors, generator'B defines the finish moment of the charge on the first said capacitor, and generator signal input terminal, three discharge tube systems A, B, and C, of which system A is under control of signals impressed on said signal input terminal, and systems B and C arerespectively under control of leading and lagging phase derivatives of said phase splitting network, each of said systems constituting devices forproducing brief surge impulses, four gaseous discharge tubes arranged in two pairs whe'reinthe anodes of each pair are capacitively intercoupled in such man- C defines the starting moment of the charge on the second said capacitor, means for so adjust ing the parameters of said'phase splitting network that generators B and C are caused to separate the charging times of the two said capacitors by a time interval equal to substantially half the sum of said charging times, a difierential relay responsive to inequalities between the charges on said capacitors, and contacts operable by'said relay for closing eitherof two circuits in said corner that the ignition of one tube causes its mate to be extinguished, ignition means for said gaseous tubes so constituted. that-one of said tubes is ignited by a surge impulse from system. i

A at the front end of a marking signal, a gaseous tube .01 the other pair is ignited hy asurge impulse from system A at the back end 'of said marking signal, and the mates to the two gaseous tubes last mentioned are ignited by a surge im- 7 pulse from system B, electrical means under control of said gaseous discharge tubes in cooperation with said system C for differentiating between two time intervals the first of which elapses'be the the moment of ignitiongof said tubes which are controlled by system B, the second time interval.

sine wave is adjusted to the cadence of said,

signals.

6. In a synchronizing system for receiving telegraph apparatus, the method of rotating the phase of a locally generated sine wave which comprises splitting the phaseoi' said sine wave to produce two components having a phase diftween the front end of said marking signal and ference of substantially 120, developing two trains of surge impulses of the same frequency as said sine wave, each train being synchronized by one of said components respectively, measuring the time lapse between the arrival of the front edge of a marking signal and the nei'ct succeeding one of said impulses in the leading train, measuring thetime lapse which starts with an impulse of the trailing train next preceding the arrival time of the back edge of said marking signal and ends with that arrival time, electrically comparing the lengths of said time measurements. and utilizing the results of said comparison to rotate the phase of said sine-wave forwardly and backwardly.

WARREN A. ANDERSON. 

